In order to maintain the stability and safe operation of an empty or partially loaded marine cargo vessel, it is necessary to add seawater to the ballast tanks to trim the vessel and/or to attain a predetermined draft.
In many instances, cargo vessels take on seawater as ballast in a first port, transport the seawater as ballast many thousands of miles to a second port, where cargo is loaded and the seawater ballast discharged into the local harbor or mooring site. It has been well documented that seawater ballast loaded at one location can contain a variety of living organisms ranging from microscopic bacteria to marine plants, fish, crustaceans and other marine life that can have a negative ecological impact when discharged into the local waters at the port of call. Although some efforts have been undertaken to reduce this problem by providing at least a crude filtration system to prevent the intake of rodents, fish, crabs and the like, these efforts have not been particularly effective.
Large volumes of water must typically be introduced into the vessel's ballast tanks and the loading must be done as quickly as possibly due to the large demurrage fees associated with the inefficient loading or idling of commercial marine vessels. Improved methods and apparatus are needed to eliminate or substantially reduce the adverse effects associated with current marine shipping practices that transport and discharge at remote locations large volumes of water that can contain biological and marine life that can have an adverse impact on the marine ecology at the point or points of discharge.
A method and apparatus that includes a bow intake conduit and that utilizes the difference in hydrodynamic pressure for effecting an exchange of water in ballast tanks while the ship is underway is disclosed in U.S. Pat. No. 6,053,121. Pressurized fresh seawater from a main conduit is introduced at the bottom of one end of a ballast tank, and a bottom drain having a valve at the opposite end of the ballast tank discharges the water through the underside of the hull into the sea. As disclosed in the '121 patent, based upon laboratory experimental data, after six hours of operation of a small-scale system, a salt water solution in the primary tank was diluted to 25% of its original salt content. There is no suggestion or teaching in the disclosure of the '121 patent that water in the ballast tank should be discharged through a port or outlet at the top of the ballast tank, nor does it disclose the desirability of the removal of biological marine life from the ballast tank.
An oxygen stripping system, such as the VENTURI OXYGEN STRIPPING SYSTEM® by NEI Treatment Systems, LLC attempts to eliminate the introduction of invasive (i.e., harmful) organisms while simultaneously protecting the vessel's ballast tanks against corrosion. This oxygen stripping system mixes very low-oxygen inert gas into ballast water as it moves through the ballast system, whereby the ballast tanks change to a deoxygenated state. Although this technique is useful in destroying harmful aquatic organisms by suffocation, this technique can causes other environmental problems by also destroying non-harmful organisms that get trapped in the ballast tanks, which is not environmentally friendly.
In commonly assigned U.S. Pat. No. 6,766,754, a ballast water inlet port is provided in the bow of a vessel, where a scoop guides the ballast water through a valve and into the tanks. The water is admitted into the scoop when the vessel is moving under a hydrodynamic pressure that is greater than the pressure of the ballast water that is to be replaced. The incoming seawater from the inlet port is directed into the bottom of the ballast tanks, where it rises to displace the existing ballast water from outlet ports located at a top portion of the ballast tanks from which it is discharged through the hull and down the side of the vessel. Although this technique is much more environmentally friendly, it utilizes a single scoop formed in the bow, which may cause drag, as well as require a substantial amount of piping that extends almost the length of the vessel to fill the ballast tanks.
It is therefore an object of this invention to provide a method and apparatus for rapidly exchanging seawater ballast from marine vessels that eliminates or greatly reduces the transport of the original ballast over great distances from the origin of the ballast, along with the marine organisms contained therein.
It is a further object of this invention to provide an efficient and economical apparatus and method for introducing fresh seawater ballast into the ballast tanks of a marine vessel while the vessel is underway and discharging ballast previously introduced and in an environmental friendly manner.
Yet another object of the present invention is to provide a method and apparatus that permits the ready control of the volume of seawater ballast, as well as its position in any one or more ballast tanks in the vessel, while minimizing the utilization of pumps and power that must be provided while the vessel is underway.
It is yet another object of the present invention to provide a method and apparatus that utilizes minimal moving parts and reduces maintenance requirements and associated costs.